This invention relates to a positively charged antimony pentoxide sol obtained by mixing an antimony pentoxide sol with an aqueous solution of a basic salt of trivalent and/or tetravalent metal and also to a process for producing the same.
Antimony pentoxide sols which have been known in the art are negatively charged on the surface of their particles. As the processes for producing such sols, there have been known the method in which an alkali antimonate is deionized with an ion-exchange resin (U.S. Pat. Nos. 3,860,523 and 4,110,247); the method in which antimony trioxide is oxidized with hydrogen peroxide under a high temperature (U.S. Pat. No. 4,022,710, Japanese Unexamined Patent Publication No. 21298/1977, U.S. Pat. No. 4,026,819); the method in which an alkyl antimonate is allowed to react with an inorganic acid, followed by peptization (Japanese Unexamined Patent Publication No. 41536/1985).
The above antimony pentoxide sols of the prior art have been utilized for various uses by making use of their microparticulate characteristics. For example, they can be used as flame retardant treating agents or flame retardant adhesives for fabrics by mixing with various resin emulsions. In order for the mixture of the sol and a resin emulsion to exhibit satisfactory flame retardant effect, the particles of the antimony pentoxide sol are required to be dispersed in the state approximate to primary particles without agglomeration as far as possible. Since the surface of the particles of the antimony pentoxide sol of the prior art is negatively charged, it can be mixed with an anionic resin emulsion comprising particles with the same negative surface charges without causing agglomeration due to repellency of charges between the particles. Whereas, when a cationic resin emulsion comprising particles with positive surface charges is mixed with an antimony pentoxide sol, agglomeration will instantly occur due to the mutually opposite polarity in charges, whereby no such mixture can be practically used.
On the other hand, an aqueous solution of a water-soluble polymer has properties such as dispersing, thickening, bonding, blocking properties, and therefore used for surface treatment of plastics, and the like. The water-soluble polymer includes polyvinyl alcohol, polyacrylamide, polyalkylene oxide and anionic or cationic polyelectrolytes such as polymers having carboxy groups, amino groups in side chains or main chains. However, the antimony pentoxide sol involve the drawback that it cannot be provided for practical use, because agglomeration occurs when it is mixed with a cationic water-soluble polymer.
Further, for example, the antimony pentoxide sol finds its use in a flame retardant acrylic fiber. By introducing antimony pentoxide colloidal particles into an acrylic fiber, there can be obtained a flame retardant fiber having high transparency and excellent dyeability, and for this purpose antimony pentoxide sol must be dispersed without agglomeration in a spinning solution of an acrylic fiber. Whereas, the antimony pentoxide sol of the prior art is liable to be agglomerated in an inorganic acid such as sulfuric acid, nitric acid, etc., and a conc. aqueous solution of an inorganic salt such as zinc chloride, sodium rhodanide, which is a good solvent for an acrylic polymer, whereby there are involved the drawbacks such that clogging of nozzle or fiber breaking may occur during spinning or that transparency of the fiber obtained is markedly lowered. For this reason, in practical application, it is required to perform a special operation such as vigorous stirring during mixing (Japanese Unexamined Patent Publication No. 142715/1980).
Further, for example, in the case of adding antimony pentoxide sol as the microfiller for the purpose of flame retardancy and increase of surface hardness into an alcoholic solution and water-alcoholic solution of a silicone resin to be used as the surface treating agent for plastic moldings or plastic films, the antimony pentoxide sol of the prior art is susceptible to agglomeration, thereby having the drawback of being lowered in transparency.